During a high pressure pressing operation of an high pressure press, a pressure medium is pressurized to a very high pressure. The pressure medium is a fluid. High pressure presses can be used in various applications. A high pressure press can for example be used for forming of sheet metal parts into predetermined shapes by highly pressurizing a fluid provided in a closed pressure vessel and use as an exerting force onto an intermediate diaphragm or the like. If the high pressure press exerts an equal pressure on every side of the contents in the pressure vessel, the press is called an isostatic press. Isostatic presses can be used for compaction or densification of metallic or ceramic powders, for reduction of pores or voids in castings or sintered articles, for sterilization and preservation of food stuffs, etc. Depending on the temperature of the pressure medium during an isostatic pressing process, the process can be called a hot isostatic pressing (HIP), a warm isostatic pressing or a cold isostatic pressing (CIP).
A pressure vessel of a conventional high pressure press comprises a cylinder body. The cylinder body is closed by closure lids at the cylinder ends. A framework is arranged to hold the closure lids at the ends of the cylinder body.
To increase the ability of the pressure vessel to resist crack formation and propagation, the pressure vessel is commonly prestressed. The vessel for example be prestressed by autofrettage, by shrinkage or by wire-winding.
The pressure level in the pressure vessel depends on the press type and the material to be pressed. In sheet metal forming the press is typically designed for pressures up to 140 MPa, in CIP for between 100 MPa and 600 MPa and in HIP for up to 300 MPa.
A cylinder for a high pressure press is traditionally manufactured by forging. A cylindrical body is first casted and subsequently forged to form a cylinder body. After a heat treatment the cylinder body is machined into its final shape and dimension. To manufacture very large cylinders put high demands on the equipments for the forging-, heat treatment- and machining processes.
Recently the demand for larger and larger sizes of the articles to be pressed has increased, implying a demand for larger and larger presses. One alternative way of producing larger presses is the manufacturing of pressure vessels with a cylinder body comprising connected sub-cylinders. The cylinder body can then comprise two or more individual sub-cylinders arranged in connection with each other, whereby the dimension of the cylinder body of the isostatic press is not limited by the manufacturing process of one single large cylinder.
Not only large presses would benefit from a cylinder body comprising connected sub-cylinders. Pressure vessels of a smaller size would with this construction have a shorter time of delivery.
A problem with such axially divided high pressure vessels, is sufficient sealing of the joint between the sub-cylinders. Leaking pressure medium may cause corrosion or difficulties regarding reaching and keeping the desired high pressures. Should pressure medium leak into the joint and be trapped, the leaked pressure medium may transfer considerable separating forces to the sub-cylinders, which may lead to damages in the connection between the sub-cylinders or even separation of the sub-cylinders.
Another problem associated with sealing arrangements in high pressure presses is that they are prone to wear and difficult to replace.